Ozone generating apparatus

ABSTRACT

An ozone generating apparatus is disclosed which comprises a power source device for feeding a rectangular waveform alternating current between the discharge electrodes of a discharge tube of an ozone generator. One or both of the output current and frequency of the power source device is controlled to overcome the disadvantages of the conventional ozone generating apparatus.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an ozone generating apparatus.

2. Description of the Prior Art

It is known that ozone can be generated by discharge and can be used invarious fields as an oxidizing agent or as a bactericide. Recently,applications of ozone have increased, especially in the field ofelimination of pollution, ozone being used for treatment of sewage,industrial drainage and nitrogen oxides NO_(x) in effluent gas.

FIG. 1( a) is a schematic view of a conventional ozone generatingapparatus where a glass discharge tube 13 is disposed in the center of ametallic cylinder 12 and a metallic electrode 14 is adhered or vapormetallized on an inner surface of the glass discharge tube 13 and isconnected to a high voltage terminal 15.

A power source 1 is connected to the high voltage terminal 15 and themetallic cylinder 12 on its outer surface so as to apply a sinusoidalwaveform voltage having a commercial or high frequency. Oxygen in theair fed from one end of the metallic cylinder 12 is converted to ozoneby the discharge in the gap between the metallic cylinder 12 and theglass discharge tube 13.

FIG. 2 is a circuit diagram of the power source system of theconventional ozone generating apparatus.

FIGS. 3( a), (b) are schematic operating waveforms of power voltage Vand current i of the ozone generator.

In FIG. 2, the reference 1 designates the power source for driving theozone generator (such as a power source having commercial frequency); 2designates a boosting transformer; 3 designates an ozone generator and 4designates a reactor for power-factor improvement.

When the power voltage is the sinusoidal waveform voltage V.sub.(t) ofFIG. 3(a), the ozone generator 3 is an equivalent capacitor whereby thephase gains π/2 (rad) from the power voltage as shown in FIG. 3(b).Accordingly, the current waveform is significantly changed during thedischarge period T_(E) and the current i.sub.(t) as a part of thesinusoidal waveform is fed during the non-discharge period T_(D).

The ozone generator can be considered equivalent to the series circuitof a capacitor C_(g) formed by the glass discharge tube 13 and acapacitor C_(a) formed by a gap between the metallic cylinder 12 and theglass discharge tube 13 as shown in FIG. 1( b). In FIG. 1( b), when thedischarge occurs in the gap, the capacitor C_(a) is considered asforming a short-circuit and only capacitor C_(g) remains in theequivalent circuit. This is schematically shown as turning on the switchS.

The operation of the conventional ozone generator will now be described.The ozone generator is considered as a series circuit of the capacitorsC_(g) and C_(a) wherein C_(a) << C_(g), in general. As shown in FIG.1(b), the voltage applied to the ozone generator is shown as V, thepartial voltage for the capacitor C_(g) is shown as V_(g) and thepartial voltage for the capacitor C_(a) is shown as V_(a).

When the sinusoidal waveform voltage V is applied to the ozonegenerator, as shown in FIG. 4, the terminal voltage V_(a) of thecapacitor C_(a) reaches the positive discharge voltage V_(s) at the timet₁ and the discharge in the gap occurs to provide O(V) of V_(a). Priorto the discharge, the terminal voltage V_(g) of the capacitor C_(g)which is formed by the glass discharge tube is not substantially changedunder the relation C_(a) << C_(g), as shown by the dotted line.

However, when the discharge occurs as the short-circuit of C_(a) at thetime t₁, all of the power voltage V is applied to C_(g) to provide V(t₁)= V_(g) (t₁) at the time t₁ and V_(g) rises to V(t₁) at the time t₁ asshown by the dotted line. The discharge is finished in a moment and thevoltage is again applied to C_(a).

The change of the voltage V of the ozone generator appears substantiallyas the change of the terminal voltage V_(a) of C_(a) under the relationof C_(a) << C_(g) and V_(g) is not substantially changed. Accordingly,the change of V_(a) is substantially the same as that of V and thedischarge occurs at the time t₂ in V_(a) = V_(s). At the time t₂, thevoltage V_(g) becomes V(t₂) = V_(g) (t₂) whereby V_(g) rises as shown bythe dotted line. The phenomenon is repeated until the time t₅.

After the time t₅, V_(a) changes substantially the same as V. However,V_(a) ≧ V_(s) is not realized until the time the maximum value of V isreached and V_(a) falls similar to the change of V until the time t₆.During this period, V_(a) is changed from positive through zero tonegative. At the time t₆, V_(a) = -V_(s) is equal to the negativedischarge voltage. At the time t₆, the discharge in the negative sideoccurs to give V_(a) = 0.

At the time t₅, V_(g) becomes V_(g) = V(t₅) and then V_(a) is kept at asubstantially constant value. However, at the time t₆, when thedischarge occurs for C_(a) to give V_(a) = 0, V_(g) suddenly falls asshown by the dotted line because V(t₆) = V_(g). After the time t₆, thesame condition is repeated to give V_(a) = -V_(s) at the times t₇, t₈,t₉ and t₁₀ and the discharges for C_(a) occur at these times to changeV_(g) as shown by the dotted line.

Accordingly, when the ozone generator is used by applying a sinusoidalwaveform voltage, the following conditions are realized.

1. In one cycle period of the voltage T_(o), the discharge phenomenonmaintaining period is 2T_(E) from t₁ to t₅ and from t₆ to t₁₀ as shownin FIG. 4 and the discharge ceasing period is 2T_(D) from t₅ to t₆ andfrom t₁₀ to t₁₁. Thus, the discharge phenomenon maintaining period isonly about 50% of one cycle period.

2. The voltage V_(a) is changed under substantially the same conditionas that of V because of a constant of ± V_(s) of the discharge voltagein the gap and the fact that C_(g) >> C_(a). Accordingly, the dischargeinterval is short around the zero point of the voltage V wherein dv/dtis high and the discharge interval increases and is longest around themaximum value of the voltage V wherein dv/dt is low.

Thus, t_(s) < t_(l) in FIG. 4.

The ozone generator operates, as stated above, in one cycle period ofthe voltage applied by the power source whereby ozone is generated. Theozone generating rate is substantially proportional to the power fed bythe power source when the conditions of the ozone generator areconstant.

The power fed from the power source to the ozone generator, that is thedischarge power W caused by the discharge of the glass discharge tube,is given by the equation ##EQU1## wherein ω= 2πf, when the averagedischarge current I_(dm) is fed and the sinusoidal waveform voltagehaving the frequency f[Hz.] is applied from the power source.

The average discharge current I_(dm) is given by the equation ##EQU2##where the discharge area of the ozone generator is S [cm² ].

Accordingly, the discharge power W is given by the equation ##EQU3##wherein E_(b) is a constant determined by a characteristic of the ozonegenerator 3 and C_(g) and C_(a) are equivalent capacitors of the ozonegenerator shown in FIG. 1(b).

As stated above, the discharge power of the ozone generator which is amain factor of the ozone generating rate is proportional to thefrequency and voltage of the power source for driving the ozonegenerator. Accordingly, in the conventional ozone generating apparatusoperated by a commercial frequency power source, the output voltage ofthe power source is changed by switching taps of a secondary side of atransformer or a voltage controlling device (not shown) for controllingthe ozone generating rate.

However, the conventional ozone generating apparatus has the followingdisadvantages.

1. The voltage applied to the ozone generator must have a waveform whichchanges dependent upon the time to cause the discharge. When the voltagewaveform is a sinusoidal waveform as is conventional, the dischargeperiod is 2T_(E) during one cycle period and the non-discharge period is2T_(D) as shown in FIG. 3 and FIG. 4. On the other hand, the power fedto the ozone generator is usually proportional to the maximum value ofthe voltage applied thereto.

2. However, when the power P_(o) is fed during the period 2T_(E) whichis realized by subtracting 2T_(D) from T_(o) as shown in FIG. 3 and FIG.4, the discharge power P_(o) is generated during the short periodwhereby heat in a concentrated condition is generated during the shortperiod. Accordingly, the yield of ozone is decreased because of therising temperature of the molecules in the gap and the discharge tubemay be damaged because of the thermal and mechanical stress of the glassdischarge tube for the ozone generator. Accordingly, in order to preventthese difficulties, the rated power of the discharge tube should bedecreased in the case of operation by application of a sinusoidalwaveform voltage.

3. Moreover, in the case of operation by application of a sinusoidalwaveform voltage, dV/dt of V(t) is changed during operation and thedischarge voltage V_(s) in the gap is constant. Accordingly, thefrequency for repeating the discharge in the initial discharge periodnear the time t₁ and t₆ is high and the frequency gradually decreases.The power is concentrated near the zero point of the power voltagethereby decreasing the yield of ozone and increasing the thermal andmechanical stress for the glass discharge tube as above-mentioned.

4. The ozone generator is an equivalent capacitor load to give a lowpower factor. Accordingly, it is necessary to connect a reactor forpower factor compensation as shown in FIG. 2 which requires a capacityfor the reactive power KV_(A) of the ozone generator.

5. In conventional ozone generating apparatus operated by a commercialfrequency power source, the voltage applied to the ozone generator ischanged by switching taps of the secondary side of a transformer or avoltage controlling device in order to control the ozone generatingrate. Accordingly, in the case of switching the taps of the secondaryside of the transformer, the ozone generating rate cannot be finelycontrolled. In the case of the voltage controlling device, a large sizeauxiliary device such as an induction voltage controlling device isrequired depending upon the increase of capacity of the ozone generatingapparatus.

6. In the case of a commercial frequency power source, the frequency isfixed. The discharge current per unit area is not changed under theapplication of a constant voltage. In order to increase the dischargecurrent per unit area, the voltage should be increased. Accordingly, alarge size apparatus including suitable insulation of the transformer isrequired.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a novel ozonegenerating apparatus which overcomes the above-mentioned disadvantagesof conventional ozone generating apparatus by feeding a rectangularwaveform alternating current to an ozone generator so as to apply anideal waveform voltage to the ozone generator and by operating the powersource under a control method having a constant voltage-variablefrequency control and/or a constant frequency-variable voltage control.

The foregoing and other objects are attained in accordance with oneaspect of the present invention through the provision of an ozonegenerating apparatus comprising a rectangular waveform alternatingcurrent feed type inverter used as a power source for operating theozone generator wherein the inverter is operated by a control methodcomprising constant voltage-variable frequency control and constantfrequency-variable voltage control to control the ozone generating rate.

In accordance with one embodiment of the ozone generating apparatus ofthe present invention, the ozone generating apparatus comprises an ozonegenerator having a discharge tube with discharge electrodes; a powersource for feeding a rectangular waveform alternating current betweenthe discharge electrodes of the ozone generator; a forward converter; areverse converter for converting the direct current of the forwardconverter to alternating current; an ozone generating rate detector fordetecting the ozone generating rate of the ozone generator to generate asignal proportional to the ozone generating rate; an adder for comparingthe output of the detector with a reference value; first and secondfunction generators to receive the output of the adder with each outputhaving predetermined characteristics; a direct current detecting circuitfor detecting DC output current fed from the forward converter to thereverse converter; a forward converter control circuit for controllingthe output current of the forward converter depending upon a comparisonof the output of the first function generator with the output of thedirect current detecting circuit; and a reverse converter controlcircuit for controlling the output frequency of the reverse converterdepending upon the output of the second function generator.

BRIEF DESCRIPTION OF THE DRAWINGS

Various objects, features and attendant advantages of the presentinvention will be more fully appreciated as the same becomes betterunderstood from the following detailed description of the presentinvention when considered in connection with the accompanying drawings,in which:

FIG. 1 shows a schematic view and an equivalent circuit of an ozonegenerator;

FIG. 2 is a circuit diagram of a conventional ozone generatingapparatus;

FIG. 3 shows waveforms for illustrating the operation of the apparatusof FIG. 2;

FIG. 4 shows waveforms for illustrating a discharge in the case of asinusoidal waveform application;

FIG. 5 shows ideal waveforms for the operation of an ozone generator;

FIG. 6 is a circuit diagram of one embodiment of an ozone generatingapparatus in accordance with the invention;

FIG. 7 shows waveforms for illustrating the operation of the ozonegenerating apparatus in accordance with the invention;

FIG. 8 shows a graph for illustrating the control operation of theapparatus of FIG. 8; and

FIG. 9 is a circuit diagram of another embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views, theembodiments of the invention will be described.

The waveform of V_(o) of FIG. 5 is an ideal drive voltage waveform foroperation of an ozone generator. The voltage V_(o) (t) rises in thepositive side in a constant gradient and suddenly falls when the voltagereaches the maximum value E_(p). Then it rises in the negative side in aconstant gradient. When such voltage is applied, the discharge occursduring almost all of one cycle of the period T_(o).

When the voltage V_(o) (t) is applied to the ozone generator, thevoltages applied to C_(g) and C_(a) are changed to V_(go) and V_(ao) asshown in FIG. 5. Moreover, the interval from the discharge to the nextdischarge for C_(a) is the same as t_(s) = t_(l) because of the constantdV_(o) /dt.

FIG. 6 is a circuit diagram of one embodiment of the apparatus of theinvention for providing an ideal voltage waveform. In FIG. 6, thereference 5 designates a forward converter for converting the commercialfrequency AC power source to a DC power source; 6 designates a DCreactor which is also used for current smoothing and for separating theDC circuit from the AC circuit; 7 - 10 designate a thyristor bridgewhich forms a reverse converter. The combination of 5 - 10 is usuallyreferred to as a rectangular waveform alternating current feed typeinverter.

The reference 11 designates a starting circuit for the current feed typeinverter which includes control means for starting. The reference 12designates an ozone generating rate detector for detecting the ozonegenerating rate and for generating a signal proportional to the ozonegenerating rate; 13 designates a reference value setter for determiningthe ozone generating rate; 14 designates an operator or adder. Thereference voltage circuit for determining the ozone generating rate isformed by 12 - 14.

The reference 15 designates a direct current detecting circuit fordetecting the current fed from the forward converter to the reverseconverter; 16 designates a function generator; 17 designates a currentcontrol circuit; 18 designates a forward converter control signalgenerating circuit. The voltage control circuit is formed by 15 - 18.

The reference 19 designates a function generator; 20 designates avoltage-frequency converter; 21 designates a signal distributor such asa flip-flop; 22 and 23 designate gate circuits of thyristors for areverse converter. The frequency control circuit is formed by 19 - 23.

The reference 2 designates a boosting transformer and 3 designates anozone generator which are the same as those of FIG. 2.

The operation of the apparatus will now be described.

In FIG. 6, the DC reactor connected between the forward converter 5 andthe reverse converter comprising the thyristors 7 - 10 usually has ahigh inductance in the current path. Accordingly, the current I_(DC)passing through the DC reactor 6 is a constant direct current as shownin FIG. 7(a).

The reverse converter comprising the thyristor bridge 7 - 10 feeds thedirect current I_(DC) under the alternate switching of the direction ofthe current to the transformer 2 and the ozone generator 3. Thus, thesubstantial rectangular waveform alternating current which is equal toI_(DC) as shown in FIG. 7(b) is fed through the transformer 2 to theozone generator 3.

The reverse converter comprising the thyristor bridge 7 - 10 feeds therectangular waveform alternating current through the transformer 2 tothe ozone generator 3 in the following normal mode of operation.

When the thyristors 7, 8 are turned on, the direct current I_(DC) is fedthrough the transformer 2 to the ozone generator 3 in one direction.After a certain period, the thyristors 9, 10 are turned on whereby thethyristors 7, 8 in the ON state are turned off by the commutation.Accordingly, the direct current I_(DC) is fed through the transformer 2to the ozone generator 3 in the opposite direction whereby the voltageV_(L) of FIG. 7(c) is generated in the primary side of the transformer2. The transformer 2 provides only a boosting voltage. Accordingly, theprimary voltage waveform V_(L) of the transformer can be considered tobe the voltage waveform of the ozone generator 3. The voltage V_(L) isapplied to the thyristors 7, 8 as a reverse voltage for the period t_(r)by turning off the thyristors 7, 8 whereby the thyristors 7, 8 arecompletely in the OFF state. On the other hand, the thyristors 9, 10 areturned off by turning on the thyristors 7, 8, and the voltage V_(L) isapplied to the thyristors 9, 10 as a reverse voltage for the periodt_(r) whereby the thyristors 9, 10 are completely in the OFF state.FIGS. 7(d), (e) show the voltage waveforms of the thyristors 7 - 10 forthe above-mentioned phenomenon in detail. When the waveforms of FIGS.7(d), (e) are on the zero line, the thyristor is in the ON state.Otherwise the thyristor is in the OFF state. The rectangular waveformalternating current is fed to the transformer 2 and the ozone generator3 by alternately repeating the turn-on and turn-off of a pair of thethyristors 7, 8 and a pair of the thyristors 9, 10 in a constant cycleperiod.

A constant current is fed to the ozone generator 3 which is anequivalent capacitor C for a half cycle period. Accordingly, the voltageV_(L) (t) generated in the primary side of the transformer 2 is given bythe equation ##EQU4## wherein V_(L) (0) designates initial voltage. Thevoltage V_(L) (t) is changed in proportion to the period.

The voltage V_(o) applied to the ozone generator 3 has a waveform whichis similar to the waveform of the primary voltage of the transformer 3and is quite similar to the ideal voltage waveform of FIG. 5. From theviewpoint of the characteristics of the ozone generator, it can beconsidered an ideal waveform and it is the optimum for the ozonegenerator.

As stated above, the direct current I_(DC) passing through the DCreactor is alternatively changed in the direction to the transformer 2and the ozone generator 3 by switching a control rectifying element suchas a thyristor. A communicating period t_(u) is required for switchingthe direction of the current. During the period t_(u), the current I_(L)is changed from +I_(DC) to -I_(DC) or from -I_(DC) to +I_(DC).Accordingly, the current waveform is not a complete rectangular waveformbut rather is a trapezoid waveform.

However, the commutating period t_(u) is usually quite short comparedwith the cycle period T_(o) for the current I_(L). Accordingly, thecurrent waveform is substantially a rectangular waveform. However, whenthe polarity of the current fed to the ozone generator is changed, thevoltage V_(L) of the ozone generator decreases to stop the discharge toform the series circuit of C_(a) and C_(g).

During the discharge period, the circuit is only C_(g) because of theshort-circuit of C_(a). However, during the non-discharge period, thegradient of the voltage drop becomes high until the time of the nextdischarge in opposite polarity because the capacitor C_(a) having onlysmall capacity is charged to the opposite polarity by the same currentsince C_(a) << C_(g). It is quite important that the voltage V_(L) bemaintained without changing the polarity just after the commutatingperiod t_(u).

After changing the direction of the direct current I_(DC), the voltageV_(L) is changed from one polarity through zero to the oppositepolarity. The period t_(r) from the finish of commutation to the timeV_(L) = 0 is usually the period for applying the reverse voltage whichis required for switching the reverse converter of the thyristor switchelement 7 - 10 from the ON state to the OFF state.

When the period for applying the reverse voltage is shorter than theforward voltage block recovery period t_(off), the switching elements inthe OFF state are switched to the ON state at the moment the voltageV_(L) is switched to the opposite polarity through the zero pointwhereby the DC power source forms a short-circuit to cause thecommutation failure phenomenon stopping the operation of the apparatus.However, the forward voltage block recovery period t_(off) of theswitching element is usually in the range of 10μs - 100μs and is quiteshort compared to the cycle period T_(o).

When the current type inverter is used as a power source for the ozonegenerator, the phase of the current gains with respect to the phase ofthe voltage to cause t_(r) > t_(off). In the current feed type inverter,the phase of the current usually gains φ = 2π f(t_(r) + t_(u) /2) withrespect to the phase of voltage.

Accordingly, if the voltage waveform of FIG. 7(c) is a sinusoidalwaveform or a rectangular waveform having the same phase, the powerfactor P.F. is cos φ. However, in the case of the waveform V_(L) of FIG.7(c), the phase of the fundamental wave component V_(L) decreasesslightly to provide a power factor of slightly less than cos φ. When thecurrent feed type inverter is used, it is unnecessary to use a reactorfor power factor compensation since it is operated at the phase angle φfor providing the reverse voltage period t_(r) which is higher than theforward voltage block recovery period t_(off) which is required for theswitching elements such as thyristors 7 - 10 used in the reverseconverter.

As stated above, the ozone generation can be effectively attained byfeeding a rectangular waveform alternating current to the ozonegenerator. However, it is desirable to have control means for freelycontrolling the ozone generating rate.

The elements 12 - 23 in FIG. 6 are provided for controlling an ozonegenerating rate proportional to the discharge power by controlling thedischarge power of the ozone generator which is the output power of thecurrent feed type inverter.

The operation of the elements 12 - 23 in FIG. 6 will now be described.

In FIG. 6, a signal voltage proportional to the ozone generating rate isprovided by an ozone generating rate detector 12 and is input to anoperator 14 wherein the signal voltage is compared with the referencevoltage of reference value setter 13 for determining the ozonegenerating rate for various purposes whereby the input signal to avoltage control circuit and a frequency control circuit is generatedfrom the operator or adder 14 to provide a detected value of the ozonegenerating rate equal to the reference value.

The ozone generating rate is proportional to the discharge power of theozone generator. The relationship W∝ f(2E_(p) -E_(b)) exists between thedischarge power W the power source voltage E_(p) and the frequency f.

In FIG. 6, function generators 16, 19 provide references of currentamplitude and frequency for controlling the ozone generating rate bychanging the current amplitude and frequency of the current feed typeinverter as the power source for the ozone generator depending upon thesignal generated from the operator 14. Thus, the function generatorreceiving the signal of the operator 14 generates an output I_(DC)proportional to the reference value in the range of the referencevoltage of O V_(r2) and generates a constant output for a higherreference voltage as shown by the full line of FIG. 8. The functiongenerator 19 generates a constant output f in a range of the referencevoltage of O-V_(r1), generates an output proportional to the referencevoltage in a range of V_(r1) - V_(r2) and generates a constant outputfor a the reference voltage higher than V_(r2) as shown by the brokenline of FIG. 8.

The output generated by the function generator 16 is input to thecurrent control circuit 17. On the other hand, the output of the directcurrent detecting circuit 15 for detecting the direct current fed fromthe forward converter 5 to the reverse converter is also fed to thecurrent control circuit 17 wherein the latter is compared with theformer.

The current control circuit 17 feeds the control signal through theforward converter control signal generating circuit 18 to the forwardconverter 5 so as to always provide equal direct current which isdetected by the direct current detecting circuit 15. Accordingly, thedirect current I_(DC) fed from the forward converter is controlled in amanner similar to the output of the function generator 16 as shown bythe full line of FIG. 8.

The output generated by the function generator 19 is converted to afrequency which is changed in a manner similar to the broken line ofFIG. 8 by the voltage-frequency converter 20. The frequency given by thevoltage-frequency converter 20 is input to the signal distributorcomprising the flip-flop 21. Two signals having 1/2 of the outputfrequency of the voltage-frequency converter 20 and having a 180° phasedifference with respect to each other are generated from the flip-flop21 and are fed to the gate circuits 22, 23 of the thyristors of thereverse converter.

The gate circuit 22 of the thyristor generates the signal of FIG. 7(f)and the gate circuit 23 of the thyristor generates the signal of FIG.7(g) whereby the pair of the thyristors 7, 8 and the pair of thyristors9, 10 are alternatively turned on and off as stated above. Thus, thedirect current I_(DC) and the frequency f are controlled with respect toeach reference value as shown by the full line and the broken line ofFIG. 8 whereby the voltage applied to the ozone generator is changed asshown by the one dot chain line of FIG. 8.

Thus, the voltage of the ozone generator is given by the equation:##EQU5## wherein I_(o) designates the current of the ozone generator andI_(o) ∝ I_(DC).

Accordingly, the voltage V_(o) of the ozone generator is controlled tobe proportional to the direct current I_(DC) under a constant frequency.When the voltage V_(o) is constant and the frequency is increased, thedirect current I_(DC) is also increased to maintain the constant voltageV_(o).

In order to protect the ozone generator from an overvoltage, thefrequency f and the direct current I_(DC) should have a maximum limitwhen the signal of the operator or adder 14 is higher than the referencevoltage V_(r2) as shown by the full line and the broken line of FIG. 8.Accordingly, the ozone generating rate corresponding to V_(r2) is themaximum ozone generating rate.

In FIG. 8, the points V_(r1) and V_(r2) of the curve or the gradient ofthe curve are determined depending upon the characteristics of the ozonegenerator 3 and the required control range of the ozone generating rate.

In accordance with the control circuit having the above-mentionedcharacteristics, the ozone generating rate is controlled by the voltageof the ozone generator under a constant frequency in a rangeconstituting a relatively low ozone generating rate. On the other hand,the ozone generating rate is controlled by the frequency under aconstant voltage of the ozone generator in a range constituting arelatively high ozone generating rate. Thus, the ozone generating ratecan be controlled in a broad range without the necessity for insulationof the ozone generating apparatus. In the control range of the ozonegenerating rate, the control of the frequency and the voltage of theozone generator can be easily performed whereby the control of the ozonegenerating rate is relatively easy and can be quite accurate.

The two dots chain line of FIG. 8 shows that the discharge power W whichis proportional to the ozone generating rate can be controlled linearly,accurately, broadly and easily by the combination of the constantfrequency-variable voltage control and the constant voltage-variablefrequency control under the relation of the discharge power W ∝ f .(2E_(p) - E_(b)).

FIG. 9 is a circuit diagram of another embodiment of the invention. InFIG. 9, the elements 2, 3, 5 - 23 are the same as those of FIG. 6 andthe effects thereof are also the same. The reference 24 designates anozone generator voltage detector; 25 designates an operator for voltagecontrol; 26 designates a frequency detector.

The voltage which is proportional to the voltage of the ozone generatoris input to the voltage control operator 25 by the ozone generatorvoltage detector 24 and is compared with the output of the functiongenerating circuit 16. The operator 25 generates an output to controlthe voltage of the ozone generator at the predetermined value given bythe function generating circuit 16 to actuate the current controlcircuit 17. Accordingly, the voltage of the ozone generator is alwayscontrolled at the predetermined value whereby stable operation of theozone generating apparatus is obtained which is effective for protectingthe ozone generator.

The frequency detector 26 detects the frequency of the current feed typeinverter for driving the ozone generator. The signal is input to thevoltage-frequency converter 20 wherein it is compared with the output ofthe function generator 19. The signal is output from thevoltage-frequency converter 20 to the distributor 21 such as a flip-flopso as to always realize the predetermined frequency. Accordingly, thefrequency is always controlled at the predetermined value and stableoperation of the ozone generator is obtained.

As stated above, in accordance with the invention, the ozone generatingapparatus has the following excellent effects:

1. The ozone generating rate can be easily controlled in a broad rangesince the discharge power which corresponds to the ozone generating rateis controlled by the constant frequency-variable voltage control or theconstant voltage-variable frequency control or a combination thereof.

2. The voltage applied to the ozone generator can be desirably low sincethe constant voltage-variable frequency control is realized in a highozone generating rate range. Accordingly, insulation can be minimizedand the apparatus can be miniaturized.

3. The discharge power can be linearly controlled by controlling thevoltage and frequency of the ozone generator in proportion to the directcurrent of the current feed type inverter. Accordingly, the ozonegenerating rate can be controlled with high accuracy.

4. A voltage similar to the ideal waveform of FIG. 5 is applied to theozone generator by using the current feed type inverter. Accordingly,the discharges occur in equal intervals during the cycle period, thepower fed to the ozone generator is uniform, the yield of ozone is highand the thermal and mechanical stress of the discharge tube aresignificantly decreased.

5. Accordingly, the rated power for a discharge tube having the samesize can be significantly increased compared with operation by aconventional sinusoidal waveform voltage.

6. The apparatus including the discharge tube can be significantlyminiaturized because of the increase of the rated power.

7. Ozone generating apparatus of large capacity can be provided.

8. It is unnecessary to use the reactor for power compensation and thevoltage adjustor required in conventional apparatus.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims theinvention may be practiced otherwise than as specifically describedherein.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:
 1. An ozone generating apparatus comprising:anozone generator having a discharge tube with discharge electrodes; apower source means for feeding a rectangular waveform alternatingcurrent between the discharge electrodes of the ozone generator; aforward converter; a reverse converter for converting the direct currentof the forward converter to alternating current; an ozone generatingrate detector for detecting the ozone generating rate of the ozonegenerator to generate a signal proportional to the ozone generatingrate; an adder for comparing the output of the detector with a referencevalue; first and second function generators to receive the output of theadder with each output having predetermined characteristics; a directcurrent detecting circuit for detecting DC output current fed from theforward converter to the reverse converter; a forward converter controlcircuit for controlling the output current of the forward converterdepending upon a comparison of the output of the first functiongenerator with the output of the direct current detecting circuit; and areverse converter control circuit for controlling the output frequencyof the reverse converter depending upon the output of the secondfunction generator.
 2. The ozone generating apparatus according to claim1 further comprising an ozone generator voltage detector for detectingthe voltage between the discharge electrodes of the ozone generator andwherein the output of the first function generator is compared with theoutput of the ozone generator voltage detector to generate a comparisonsignal to the forward converter control circuit.
 3. The ozone generatorapparatus according to claim 1 wherein the reverse converter controlcircuit comprises a frequency detector for detecting the outputfrequency of the reverse converter and wherein the output of thefrequency detector is compared with the output of the second functiongenerator to control the output frequency of the reverse converter inaccordance with the comparison.
 4. An ozone generating apparatuscomprising:an ozone generator having a discharge tube with dischargeelectrodes; power source means for feeding a rectangular waveformalternating current through the discharge electrodes of the ozonegenerator; and control means for controlling the ozone generating rateof the ozone generator; wherein the power source means comprises acurrent feed type inverter comprising a forward converter for obtainingdirect current from an AC power source, a reverse converter forconverting the direct current of the forward converter to alternatingcurrent and a DC reactor connected between the forward converter and thereverse converter; and wherein the control means comprises an ozonegenerating rate detector for detecting the ozone generating rate of theozone generator to generate a signal proportional to the ozonegenerating rate, an adder for comparing the output of the detector witha reference value, a function generator to receive the output of theadder with the output thereof having predetermined characteristics, adirect current detecting circuit for detecting DC output current fedfrom the forward converter to the reverse converter, and a forwardconverter control circuit for controlling the output current of theforward converter depending upon a comparison of the output of the firstfunction generator with the output of the direct current detectingcircuit.
 5. The ozone generating apparatus according to claim 4 whereinthe reverse converter is a static type converter comprising one or morethyristors.
 6. The ozone generating apparatus according to claim 4wherein the forward converter is a static type converter comprising oneor more thyristors.
 7. The ozone generating apparatus according to claim4 further comprising a starting circuit for feeding energy forcommutation of the thyristor of the reverse converter to the ozonegenerator wherein the reverse converter comprises one or morethyristors.
 8. An ozone generating apparatus comprising:an ozonegenerator having a discharge tube with discharge electrodes; powersource means for feeding a rectangular waveform alternating currentthrough the discharge electrodes of the ozone generator; and means forcontrolling the ozone generating rate of the ozone generator; whereinthe ozone generating rate controlling means comprises an ozonegenerating rate detector for detecting the ozone generating rate of theozone generator to generate a signal proportional to the ozonegenerating rate, an adder for comparing the output of the detector witha reference value, a function generator to receive the output of theadder with the output thereof having predetermined characteristics, andmeans for controlling the frequency of the rectangular waveformalternating current depending upon the output of the function generator.